Can it be? Yes! They're shouting at him! "Put the microphones down! We can't see you!"

Harry Truman, wearing a white linen suit, peers out at the delegates. It's 1948. Two o'clock in the morning. He's trying to start his speech at the Democratic National Convention in Philadelphia. So far, it's been humiliating.

First, he knows he's a terrible speaker – so bad his aides now give him talking points, hoping he'll be livelier when he ad-libs.

Worse, most delegates don't like him. Truman knows they want to draft the most popular person in the country, Gen. Dwight Eisenhower. Only the political bosses running their delegations have kept them in line.

And the Southern Democrats? With a civil rights plank in the platform, they've walked out, likely to form a third party, which everybody thinks will doom his chances.

Even little things backfire. Just as he got to the stage, a woman rushed up to present him with a cage containing "doves of peace." They were pigeons. They got loose, flew up to the rafters and, as an aide wrote later, "did what pigeons do."

Today, 64 years later, the Republicans and Democrats are gearing up to gavel in their conventions in a way that will allow them to control every picosecond of the multiday events.

When the Republicans open their conclave on Aug. 27 in Tampa, Fla., and the Democrats a week later in Charlotte, N.C., they will try to make everyone stay on message and stick to their meticulously prepared scripts in what has become one of the most tightly controlled rituals in American politics.

But since the first Democratic convention in 1832, these quadrennial events have always been full of surprises. These may be, too.

That's not to say there's any doubt about the outcome. Longtime GOP strategist Joe Gaylord ran the rules committee for the 1976 Republican National Convention – the last convention when it wasn't clear who would be the nominee.

"That was a raucous event," says Mr. Gaylord, who went on to play major roles at five more. "Now, it's such a managed stage show."

Certainly viewers will hear about big issues. This election pits a nominee who wants to carry out the 2010 health-care act against one who wants to repeal it; one who'll work for same-sex marriage against one who'll try to keep marriage between a man and a woman; one who would repeal tax cuts for millionaires against one who would make those tax cuts permanent; one who would continue a government-run Medicare program against one who might convert it to a voucher-based system.

Washington will spend about $15 trillion in the next four years. Mitt Romney and Barack Obama have different ideas about where that money should go. The conventions can highlight some of those differences.

Still, the changes in how conventions work and what they do have made people question the value of these events, which received $18 million each in federal subsidies this year, in addition to the $50 million Washington gives each host city for security. In 1996, Ted Koppel, then the popular host of "Nightline," left the Republican convention in San Diego early.

"More of an infomercial than a news event," he said, arguing that gavel-to-gavel coverage of them wasn't useful anymore.

Is that true? Does knowing who the nominees will be really mean there's no news worth reporting? How exactly have conventions changed over the years? Are they still important?

* * *

Asking whether conventions are important is not the same as asking whether they've reflected important things. There's no doubt that since 1832, each of the 44 Democratic and 37 Republican conventions has featured clashes over wrenching national issues.

The fiercest early battles took place with no spectators and no formal speeches. They usually revolved around slavery: In 1852, after three successive Democratic conventions filled with bitter debate, the exhausted delegates passed a resolution ordering the party to resist any more discussion of "the agitation of the slavery question under whatever shape or color the attempt may be made."

The history of those early conventions is full of compromise, conflict, and, well, deals. Take 1860, when the newly formed Republican Party held its second convention.

The favorite going in: New York Sen. William Seward. But Seward was bitterly antislavery. In those days, Americans thought it unseemly for nominees even to attend the convention. Abraham Lincoln, waiting back home in Springfield, hoped that if Seward didn't win on the first ballot, delegates might switch to someone more moderate – like him. Also in the running: Ohio Sen. Salmon Chase.

By the third ballot, Lincoln was still behind. He had not authorized any horse-trading. But at that point, Chicago publisher and Lincoln backer Joe Medill leaned over and whispered to the Ohio state chair: "Switch your vote. Chase can have anything he wants!"

A deal! The Ohio chair jumped to his feet and got three others to switch their votes, setting off a Lincoln stampede. Delegates began stomping their boots. Up on the roof someone fired off a cannon. Church bells rang. Riverboats tooted, and soon Lincoln was reading a telegram with the results.

"You better shake my hand while you can," he said to people with him. "Honors elevate some men." Later, Lincoln made sure to elevate Chase. He named him Treasury secretary.

Like Lincoln, other 19th-century nominees avoided the conventions. It wasn't until 1924 that one would even deliver an acceptance speech. But in 1896, politicians saw how electrifying the well-prepared convention speech could be.

The country had plunged deep into a depression. Both Southerners and Westerners believed in "bimetallism": having the dollar backed by silver as well as gold. This, they argued, would enlarge the money supply and allow farmers to sell their crops for more money.

The national champion of bimetallism, former Nebraska Congressman William Jennings Bryan, came to the convention in Chicago intending to speak about his pet issue.

He started softly. But as he began talking about farmers, the hall exploded. When he mentioned miners, the cheers were so thunderous he couldn't go on.

At the end, he bellowed the now-famous lines: "You shall not press down upon the brow of labor this crown of thorns. You shall not crucify mankind upon a cross of gold." Putting both hands to his head, Bryan stretched out his fingers – like the crown of Jesus. And held that pose for five seconds.

Delegates hurled their coats in the air, then rushed over to lift Bryan on their shoulders and paraded him around for a half-hour – and the next morning made the 36-year-old the nominee.

Michael Berman remembers a more recent speech set against a backdrop of passion. Now president of a big Washington lobbying firm, Mr. Berman played organizing roles in seven Democratic conventions.

But in 1968 he was a young staffer to Minnesota Sen. Walter Mondale. The country was torn over the Vietnam War. Outside the Democratic National Convention, also in Chicago, police tear-gassed, beat, and arrested demonstrators – one report called it a "police riot."

Ribicoff looked into the crowd at Daley. "And if George McGovern were president," he cried, "we would not have Gestapo tactics in the streets of Chicago!"

Daley jumped to his feet slashing a finger across his own neck, shouting words this magazine can't print. It was a madhouse.

* * *

"I was tear-gassed," says Berman. He doesn't make a big deal of it. Lots of people were.

In his organizing heyday, Berman got annoyed when Democratic graybeards would tell him to run conventions the way they had back in the old days. After the 2004 convention, his wife said, "You're not doing this anymore."

Why not? "Remember those old-timers telling you how to run the '84 campaign?" she asked. "It's somebody else's turn." He's no longer involved. Who better to assess what's changed since 1968?

"The candidates are elected long before we get there," Berman says, for openers. "I don't think anyone cares about the platform.... It used to be you were gathering together the party organization. But now [we] elect delegates. They're not part of the party structure."

He adds, "And communication changed."

Let me interpret: The basic tasks at conventions have stayed the same for decades. The participants examine delegates' credentials, decide on rules, vote on a party platform, then nominate and choose candidates in what for 48 years has been a four-day event.

But Berman is summarizing two big changes. First, the rise of primaries – and consequent decline in the power of party bosses. That transformed what kind of delegates came to the convention.

How did that happen? In one reasonably accurate word: Vietnam. While Democrats nominated Hubert Humphrey in 1968, the party was so fractured over the war that the winners tried to placate the anti-Vietnam faction by allowing McGovern to chair a commission recommending changes in the nominating process. Then, in a fit of idealism, it adopted them.

It had already been years since candidates went to a "brokered" convention, where party bosses, controlling most of the delegates, traded votes to pick a nominee. The last Republican multiballot convention was in 1948, and for the Democrats, in 1952.

The McGovern Commission recommendations, many of which Republicans adopted, too, paved the way for an increase in presidential primaries. They've risen from 14 in 1968 to 39 in 2012. That didn't just dim the chances of a brokered convention. Primaries forced candidates to enter and win delegates while the media breathlessly reported their rising totals.

The last time delegates arrived not sure who the nominee would be was the GOP convention in 1976, when it seemed as though Ronald Reagan might beat then-President Gerald Ford.

"Every seat filled an hour before the proceedings," Gaylord remembers. "Nancy Reagan comes into the hall and the place erupted. Betty Ford comes in – same thing. I'll never forget when the first person for Ford got up. Cheers and boos for 10 minutes."

Since then, there's been no such suspense. This year Mr. Romney effectively clinched the nomination after winning the Texas primary May 29.

The changes in communication have been no less dramatic. The first convention broadcast over radio came in 1924 – when only 60,000 Americans owned a radio. When Truman got up to speak in 1948, some 347,000 homes had TVs. By 1960, close to 35 million Americans watched John F. Kennedy's acceptance speech; 100 million watched all or part of both conventions. And in 2012?

"Forget Twitter," Berman says. "Add up Facebook and PBS, Internet, CNN. Anyone interested can find coverage." Suddenly, candidates became far more interested in talking to those at home than to those in the convention hall.

Freed of the nomination battle, able to reach millions of voters at fiber-optic speed, candidates can't resist making conventions exactly the infomercial Mr. Koppel described. But is that necessarily a bad thing?

GOP pollster David Winston demurs. "If you just want to know who's the nominee? Yeah, then it's an infomercial." But like many other experts, Mr. Winston makes clear that there are far more valuable things about the conventions than finding out who the nominees are. He puts himself in the shoes of a voter. "I'd look at it this way: What is this party presenting to me? Do they understand [me]?"

Democratic pollster Geoff Garin, Winston's opponent in many campaigns, agrees. "You really ought to think of a convention not as a one-off event," he says, "but a place where a candidate and party make a core argument."

* * *

Watching a political party discuss ideas, though, doesn't necessarily determine your vote, any more than sticking a peach pit in the ground produces a tree.

Lots of other things matter: the state of the economy, how the candidates fare in what Mr. Garin calls that "other made for TV event" – the debates – and big news events. In 2004, Winston recalls, George W. Bush's convention speech was about national security. The next day came the school massacre in Chechnya, which, he says, helped lock in the support of mothers worried about security.

Perhaps the most important influence: what a candidate believes. Republican consultant Stuart Spencer has argued that the politicians with the most longevity are those who say, "This is where I stand."

The great majority of voters who will watch the conventions believe they know where Mr. Obama and Romney stand, and agree. They've made up their minds. But a convention can reinforce their views of a candidate's character and convictions – and help sway undecideds.

"It's like the opening moves in a chess match," says Winston, an avid chess player. "We begin to see how they frame up the election."

The candidates will differ on the issues. But they'll both aim, among others, for four things.

•Balance problems and solutions.

"They have an obligation to present the future. What would a Romney administration mean for America? You can't just say Obama's terrible," Gaylord says.

"Voters," Garin says, "hunger to hear not just what's wrong with the other guy but if anyone holds out hope for fixing serious problems."

•Be likable.

Aristotle knew this 2,500 years ago. Persuasion, he wrote, involves logos (logic), pathos (emotion), and ethos (character). Voters must like the nominee.

"Not to be unkind," Gaylord says, "but part of the Romney strategy should be to show his humanness." Is Romney just a stiff, rich, white guy who doesn't know what real people are like?

"Expect a lot of his sons, wife, people who can tell stories of him," Gaylord says.

Convention organizers focus most intently on the problems of their base. But since different groups may have different problems, both parties will try appealing to them one at a time.

One such target: Hispanics. Strategists in both parties believe winning over this rapidly growing group could heavily influence national elections for decades. In addition to appeals targeting women, African-Americans, and gays, look for more appeals from Spanish-surnamed speakers, mispronounced Spanish phrases, or revised ideas about immigration.

•Focus on swing states.

Sorry, most voters. For Romney and Obama, this election is not about you. Right now, both campaigns know almost exactly how 41 states will vote. They are fighting over the remaining nine. Those states account for 115 electoral votes – 70 of them in Pennsylvania, Ohio, Virginia, and Florida alone. Look for attention and speakers appealing to issues especially vital to these Big Four.

Meanwhile, here's what convention planners will try to make sure you won't see in 2012: intraparty squabbles. Like platform fights.

Platforms are fascinating and useful. They remind you that at one point Republicans were the party of antitrust legislation, and in 1972 supported the "statesmanship of the labor union movement." They remind you that Democrats once wanted to restrict immigrants from China but not other "worthy" nations, wanted to cut government spending (1904), and supported the Ku Klux Klan (1924).

"In 1980," Garin remembers, "significant platform fights were coming to the floor. Delegates took those seriously. We don't have those anymore. Conventions aren't party functions. They're for the nominees."

Still, though conventions no longer decide nominees and keep platform debates out of public view, does that mean they're irrelevant?

Berman has become deeply skeptical about their value.

"It's the most significant waste of money spent in presidential campaigns," he says. "Hundreds of millions spent to what end?"

Winston casts a qualified vote for conventions, but he has reservations, too. "I don't know if you need the four days," he says.

"It's good to devote eight hours every four years to present our best light to the American people," Gaylord says. He adds, "We probably should get rid of federal funding."

Actually, the conventions are already changing. After staging an outdoor festival the first day, the Democrats will meet in Charlotte's Time Warner Cable Arena for just two days. Obama will then accept his nomination on the final day in a football stadium, just as he did in Denver in 2008.

Flawed though conventions are, experts offer a few suggestions for people tuning in.

•Listen for solutions.

One way to do this: Use a four-box grid popular with political consultants, two boxes each for what the two parties say about themselves and their opponents. Campaigns are often about exaggerating small differences – the difference between the Obama and Romney plans on government spending are only about 2 percent of gross national product. A chart can help you see the differences.

"It tells you what they're going to do," Gaylord says, noting it can help clarify whether a nominee is believable or not. Gaylord mentions President Ford's in 1976. His voice softens as he quotes the line he still remembers: "It's from you I come and with you I stand.' "

Garin points out that an effective acceptance speech is also what candidates need. "You want people feeling energized," he says. "Great speeches have that effect."

Even Berman, dubious as he is about the whole process, agrees. What do candidates need to do? "Give a good speech. The rest is folderol."

* * *

Ever since William Jennings Bryan stepped to the podium in 1896, speeches have become a way to fuse intellect and emotion. They give conventions their drama. They are what people remember.

And the best speeches may not belong to the nominees. The Democrats lost in 1984, but Garin calls that year a "rhetorical high point for Democrats," mentioning addresses by Mario Cuomo and Jesse Jackson. A big speech can propel little-known politicians into national politics – Obama in 2004, yes, but also Humphrey in 1948 and Ronald Reagan in 1964.

The way listeners react to political speeches usually depends on the views of those making them. We don't care about Shakespeare's politics when we watch "Macbeth." But no matter how imaginatively a Republican uses language, a Democrat hearing it will grimace.

At times, though, words transcend politics. There's one such moment in Arnold Schwarzenegger's 2004 Republican convention keynote. Early in the speech he tells how he and his family were stopped at a checkpoint when the Soviets still occupied Austria.

"We didn't have a car," he says. "We were in my uncle's car. It was near dark as we came to the Soviet checkpoint."

The audience, which has been cheering every line, falls silent. "I was a little boy. I was not an action hero then," Mr. Schwarzenegger says. "I remember how scared I was that the soldiers would pull my father or my uncle out of the car, and I would never see them again."

Suddenly, even Democrats see him, not as the Terminator, not as a Republican, but as a scared little kid in the back seat.

And no matter what your views, when it comes to sheer emotion, few speeches rival the one little-known Mary Fisher gave at the 1992 Republican convention.

It was still a time when mentioning AIDS was the third rail of American politics. Politicians pretended it didn't exist, or came from immoral acts. Ms. Fisher was the mother of two kids. She had tested positive for HIV, having gotten it from her ex-husband.

Republicans allowed Fisher a few minutes at the podium. "I have come tonight to bring our silence to an end," she began. "I want your attention, not your applause."

Obediently, most delegates fell silent. After a few minutes came the first, small smattering of applause. It grew louder when she told the delegates she felt blessed by her supportive family. Then she spoke directly to those who weren't that blessed.

"You are HIV positive, but dare not say it. You have lost loved ones, but you dare not whisper the word AIDS. You weep silently. You grieve alone. I have a message for you. It is not you who should feel shame. It is we."

When she finished, there were no waving signs. No whoops. But the delegates rose to their feet, including a somber Gerald and Betty Ford. The applause was loud – and long.

If you watch the black-and-white film that survives of Truman's address, you can tell from the way he repeats himself ("As I said before") that he is following an outline. But he's full of energy, merrily uttering things no aide would allow today.

Today, you don't admit your own voters might do something stupid. Truman says Democrats have helped farmers so much that "if they don't do their duty by the Democratic Party, they are the most ungrateful people in the world!" Today, a president leaves vitriol to surrogates. Truman says the "rotten" GOP tax bill "sticks a knife into the back of the poor."

Then, with pigeons still circling overhead, to the amazement of his aides, Truman ad-libs something. On what Missouri calls "Turnip Day," he says, he will call a special session of Congress – the Turnip Session. He'll see if Republicans will do what people need.

Republicans were flummoxed. What was Turnip Day? It turned out that's when Missouri farmers had to plant the turnips no matter what – a sanitized version of a saying that ends with "get off the pot."

"I'm not going to give that fellow anything," fumed a leader of the opposition, GOP Sen. Robert Taft of Ohio.

Republicans decided to sit on their hands during the special session. It turned out to be a colossal mistake. Truman had turned disaster into triumph in Philadelphia. He ran against a "do-nothing Congress" and pulled out a victory no one thought possible.

More than a century after Bryan stepped to the podium, and 64 years after Truman, speeches still matter. At the upcoming conventions, some speeches will offer clichés and distortions. Some will bring insight to issues. Some will show us a politician articulate enough to become memorable even when speaking from a teleprompter. Some will offer us only a single memorable phrase.

But, then again, we might hear something that will stay with us for a lifetime – even if it isn't in the script.

• Robert A. Lehrman is a novelist and former chief White House speech writer for Vice President Al Gore. Author of 'The Political Speechwriter's Companion,' he teaches at American University and co-runs a blog, PunditWire.